Radioactive decay - waves and particles Study Guide

Radioactive decay is a random process by which unstable atomic nuclei lose energy by emitting radiation. This process is spontaneous and cannot be influenced by external factors such as temperature, pressure, or chemical reactions. The rate of decay is measured by the activity of the sample, which is the number of decays per second, typically measured in becquerels (Bq). A key concept in radioactive decay is half-life. The half-life is the time it takes for half of the radioactive nuclei in a sample to decay, or equivalently, the time it takes for the activity of the sample to halve. It is a constant value for a given isotope. After one half-life, the fraction of the original radioactive nuclei remaining is 1/2. After two half-lives, it's 1/2 * 1/2 = 1/4. After three half-lives, it's 1/2 * 1/2 * 1/2 = 1/8, and so on. In general, after 'n' half-lives, the fraction of the original radioactive nuclei remaining is (1/2)^n. The net decline refers to the fraction of the original nuclei that have decayed. If (1/2)^n remains, then 1 - (1/2)^n has decayed. This net decline can be expressed as a ratio. For example, if 1/8 remains, then 7/8 has decayed. The ratio of decayed nuclei to original nuclei would be 7:8. This calculation is crucial for understanding how the amount of a radioactive substance changes over time and its implications in various applications like carbon dating, medical diagnostics, and nuclear waste management.

Radioactive decay involves unstable atomic nuclei transforming into more stable forms by emitting radiation. These processes can be represented by nuclear equations, which must be balanced in terms of both mass number (the total number of protons and neutrons) and atomic number (the number of protons, which determines the element and its charge). For alpha decay, a nucleus emits an alpha particle, which is essentially a helium nucleus (two protons and two neutrons). This means the parent nucleus's mass number decreases by 4 and its atomic number decreases by 2, forming a new element. In beta decay, a neutron within the nucleus converts into a proton, emitting a high-energy electron (beta particle) and an antineutrino. This process increases the atomic number by 1, as a new proton is formed, but the mass number remains unchanged since a neutron is replaced by a proton. The emission of a beta particle means the nucleus effectively gains a positive charge, with the beta particle carrying a negative charge. Gamma radiation, unlike alpha and beta, is electromagnetic radiation, not a particle. It is emitted when an excited nucleus releases excess energy after other decay processes, returning to a lower energy state. Gamma emission does not change the mass number or atomic number of the nucleus, so it does not transform one element into another, but rather makes the existing nucleus more stable.